It's the season to be on the lookout for enormous white birds, otherwise known as whooping cranes, as they begin their migration to their wintering grounds.

As many as 230 of the endangered birds are expected to make the 2,500-mile flight from Wood Buffalo National Park in far northeastern Alberta, Canada, to the marshes around Aransas National Wildlife Refuge on the Texas Gulf Coast. To get there, many of the birds will pass through North Dakota.

"A lot of times they are in areas where sandhill cranes are. Sometimes they are mixed in or in areas where sandhills frequent," said Paul Van Ningen, the manager at Long Lake NWR near Moffit. The refuge sometimes is a stopover point for migrating whooping cranes.

That whooping cranes often travel with the smaller sandhills presents potential red flags for anyone hunting sandhills: The big white bird, protected under the Endangered Species Act, is off-limits. Sandhill crane season opened Saturday.

Whooping crane adults are white with black wingtips that are visible only in flight, while juveniles have a mixture of white and brown body feathers. In flight, whoopers' long necks are extended straight forward, and their legs stick out past their tails. They have a wingspan of about 7 feet, and at more than 4 feet, they are North America's tallest bird. They typically fly singly or travel in flocks of two to four.

Things to note for anyone who sees a whooping crane are the location, the date, the number of adults and juveniles and if leg bands are visible. Reports help biologists locate important whooping crane habitat areas, monitor marked birds, determine survival and population numbers and identify times and migration routes.

To report a sighting, contact the U.S. Fish and Wildlife Service at Long Lake NWR at 701-387-4397 or gregg­;_knutsen@;fws.gov, or the North Dakota Game and Fish Department's main office at 328-6300 or a local game warden.

Most fall observations are associated with whoopers that are feeding.

"They spend a lot of time in small-grain fields or somewhere where corn is cropped or harvested," Van Ningen said. "They are rarely seen in wetlands. That's more in the spring. If you see one in a wetland, it's usually morning or evening."

The arrival of 230 whooping cranes in the Aransas NWR area would be a record, topping the 217 whoopers that wintered there in 2004-05.

However, heavy rains in Wood Buffalo took a toll on many sets of twin chicks. An aerial check of seven of the 14 twin pairs after the rains found that only one set of twins had survived, five pairs had lost one chick, and one pair had apparently lost both chicks. The other seven pairs of twins were not checked, meaning the number of surviving chicks could be lower.

There already has been one unconfirmed whooping crane sighting in northern North Dakota, Van Ningen said. That came on Sept. 2. The last week of September is usually when the first reports of whooping crane sightings come in.

(Reach reporter Richard Hinton at 701-250-8256 or richard.hinton@;bismarcktribune.com.)